Current ultrasonic imagers and flow measurement systems cannot process echoes from capillary blood, because these are 'drowned out' by the much stronger echoes from the surrounding tissues. In this research we propose to apply a new method for separating capillary blood echoes from tissue echoes, so as to estimate blood flow in small vessels and tissue perfusion, in connection with tumor detection and evaluation. This method separates capillary blood echoes from tissue echoes by using the second-harmonic echo of the ultrasonic contrast agent LEVOVIST/TM, and has been used by us, to ultrasonically detect capillary blood and blood flow in the rabbit. The project includes the following goals: 1. Develop an improved version of our intersecting beam second-harmonic transducer, and use it to characterize the contrast agent and obtain dose-response curves, relating the concentration of the agent to the 2nd harmonic echo strength and the degree of tissue perfusion. Compare tissue perfusion estimates in animals using contrast, with gold standard methods such as radioactive microspheres. 2. Modify an existing medical imager to obtain 2nd harmonic Duplex, B- mode and Color Doppler operation. The Duplex mode will make it possible to show the anatomical site where tissue perfusion is being measured, the B-mode will make it possible to observe tissue brightening corresponding to perfusion during the passage of a bolus of contrast, and the Color Doppler mode will enable the visualization of vessels too small to be detected at present which are believed to play a role in tumor growth. 3. Verify the safety and effectiveness of these systems in animals, and then attempt to detect blood flow patterns associated with liver cancer in woodchucks, as well with breast and liver cancer in humans.